1. Field of the Invention
The present invention relates to a technology for processing an image captured by an optical system having a wide angle and a large distortion.
2. Description of the Related Art
Recently, demands for a wide-angle imaging apparatus are increasing for applications such as a back monitor of a vehicle. However, as the angle becomes wider, the chromatic aberration of magnification and distortion become large, making it difficult to design an optical system with a small aberration. Therefore, performance needs to be improved in combination with image processing.
In the imaging apparatus using the optical system having the chromatic aberration of magnification and the distortion, a conventional technique for correcting a distortion includes a method of correcting the chromatic aberration of magnification and the distortion at the same time by performing coordinate transformation independently for each color component of red (R), green (G), and blue (B) with respect to an R-signal, a G-signal, and a B-signal obtained by the imaging device such as a charge coupled device (CCD) or a complimentary metal oxide semiconductor (CMOS) sensor at a subsequent stage, as described in Japanese Patent Application Laid-open No. 2006-345054. Also, it is well known that a method of correcting only the distortion by performing coordinate transformation for respective color components of RGB together, ignoring the chromatic aberration of magnification. Further, a complicated polynomial or the like is generally used as the formula of coordinate transformation, for example, as described in Hatanaka, et al., “Development of In-Vehicle Image Processing Equipment”, SEI Technical Review, Vol. 162, pp. 90-93, March 2003 [http://www.sei.co.jp/tr/pdf/automotve/sei10357.pdf].
Although the magnification chromatic aberration is different for each color component, the distortion is uniform in respective color components of RGB. Further, the distortion is much larger than the magnification chromatic aberration. Therefore, it is desired to correct the magnification chromatic aberration and the distortion separately.
However, in correction of the distortion, coordinate transformation is conventionally performed in x and y directions, and a complicated polynomial or the like is generally used as the formula of coordinate transformation. Therefore, the circuit size increases, and there is a limitation in cost reduction. Particularly, in order to correct a fisheye image having a large distortion obtained by using the fisheye optical system to an image easily viewable to human eyes, a complicated polynomial is required, thereby causing an increase in the circuit size. The fisheye optical system refers to an optical system that executes projection methods such as stereographic projection y=2f tan(θ/2), equidistant projection y=fθ, equisolidangle projection y=2f sin(θ/2), and orthogonal projection y=f sin θ other than a projection method in a normal lens y=f tan θ, where an image height is y, a focal length is f, and a half view angle is θ.